The invention relates to an inner ring for a guide vane cascade, an inner ring sector for an inner ring, a guide vane cascade having an inner ring and a plurality of guide vanes, as well as a turbomachine having a guide vane cascade.
Turbomachines, such as aircraft engines and stationary gas turbines, often have at least one compressor-side row of guide vanes having a plurality of guide vanes for the adjustment of optimal operating conditions. The row of guide vanes forms, together with an inner ring, a so-called guide vane cascade. Preferably, these guide vanes can pivot around their longitudinal axis.
The adjustable guide vanes can be actuated via radially outer-mounted adjusting pins of the guide vanes, the adjusting pins being able to interact with a corresponding adjusting device on the outer casing. A seal support, which is furnished with sealing elements or run-in coatings that lie opposite to rotor-side sealing ribs, is preferably carried on the inner ring.
The inner ring preferably has a plurality of bearing mounts extending in the radial direction, into each of which a guide vane plate of a guide vane is inserted or can be inserted. The radially inner end of a guide vane is stabilized by such a guide vane plate arranged in the bearing mount. In this case, the axis of rotation of the adjustable guide vane is perpendicular to the central axis of the guide vane cascade or the inner ring thereof. The guide vane plate can have a bearing journal on its radially inner side and the bearing mount can be arranged so as to accommodate this bearing journal together with an associated bushing.
The bearing mounts in the inner ring are separated from one another in the peripheral direction by respective separating walls extending in the axial direction. During manufacture of the inner ring as well as during operation of the guide vane cascade, there is the danger that such a separating wall will partially give way and thus be pressed into an adjacent bearing mount, which, as a result, would no longer retain its exact form; this can be prevented or at least impeded by a provided bearing mount of a guide vane plate and/or a pivoting of the guide vane. In operation, the separating wall can also be bent in the direction of an adjacent bearing mount and thus impair the ability of the guide vane inserted therein to pivot.
In order to minimize the danger of such a deformation of the bearing mounts, conventional inner rings are therefore fabricated with a minimum wall thickness for the separating walls, which the latter must have at their thinnest points.
For a given inner ring circumference, the number of bearing mounts for guide vane plates (and hence the number of mountable guide vanes) is determined by the given blade plate sizes as well as the minimum wall thickness that is to be maintained. These parameters accordingly act to limit the design of a turbomachine having a large number of pivotable guide vanes or large guide vane plates. However, such a design and/or a minimum size of the guide vane plate are or is often advantageous in terms of aerodynamics and/or structural mechanics.
The publication WO 2014/078 121 A1 discloses an arrangement in which the bearing mounts are not separated from one another by separating walls, but instead the depressions for the guide vane plates are arranged at a radially outer inner ring surface so as to transition into one another.
This has the drawback of increased leakage between the bearing mounts for the guide vane plates and all the way through them. In addition, a centering of the guide vane plates can be unstable in such an arrangement.